Patent GB-302301-A (GB)
Title: Improved call-finding arrangements in automatic telephone systems
IPC: H04Q3/00
Filed: 1927-09-14
Abstract: 302,301. Siemens & Co., Ltd., Hum-. phries, H. E., and Dixon, R. G. Sept. 14, 1927. Automatic exchange systems.-In a system employing bi-directional call-finders, each call-finder is assigned to a particular level opposite which its wipers stand when not in use, and has preference in dealing with calls over that level. When the finder or finders assigned to a level are in use, preference in dealing with a further call in the level is given to a finder assigned to the level next below, and so on, the finder taken into use being always the one which has the least number of steps to take to reach the calling line. The call-finders are provided with vertically moving wipers V1, V2, one to determine when the assigned level is reached, a. connection being made to the appropriate terminal of the set NP1, the other to determine when the level of the calling line is reached, the corresponding terminal of all the sets NP2 being marked by a level marking relay. The level marking relay also grounds the common circuit 20 which is connected over shelf contacts 15 to the starting circuit 13 of the finder assigned to the level in which the calling line appears. If this finder is in use, the connection is extended over wire 14 to the starting circuit of the next finder, and so on until an idle finder is reached. If there are more than 10 call-finders in a shelf, some levels have more than one finder assigned to them. When a finder is removed from the shelf, the common circuit is extended by bridging contacts' 15 as shown at 18. A statistical meter may be operated when all the finders are in use. As shown, the call-finders have two sets of wipers which test simultaneously. Calling line in the assigned level. Assuming this to be the 7th level, level marking relay LM7 energizes over a front contact of the line relay and grounds wire 13 and the 7th terminal of the set NP2. Start relay B (winding 1) energizes, looks over winding 2 in series with relay C (winding 1) to wiper V2 and connects up relay A which was previously short-circuited. The rotary magnet RM operates to step the wipers over the assigned level. The calling line is marked by battery (through the cut-off relay) on the test terminal, and when this is reached, the corresponding switching relay D or E energizes, locks in series with relay F (winding 1) and cuts the drive. In the case of simultaneous calls from lines connected in the same position in the two banks, priority is given to the upper bank by making relay D quicker in operation than relay E, contact d7 opening the holding circuit of the latter. Relay F releases relay A, closes a holding circuit for relay C (both windings) over wiper VI, and complete a short-circuit about relay G (winding 2) also over wiper VI. Level marking relay LM<7> falls back when switching through occurs, and relay B relapses, extending the starting circuit 13 over contacts f<1>, b7 and wire 14 to the relay B of the next call-finder. When release takes place, relays D, F fall back in succession, and in the interval the rotary release magnet RZM operates. Relay C relapses, and the callfinder is ready to deal with another call. If the subscriber hangs up before his line has been found, level marking relay LM<7> falls back, releasing relays C, B, A and the rotary release magnet RZM operates. Should a subscriber hang up before his line has been found, and should another line in the level which has already been passed over by the wipers call at this time, the rotary movement continues until the last terminals are reached, when relay E energizes over test wipec C<2> and connects up relay F. Relays A, E, B fall back and the rotary release magnet RZM operates. Calling line not in the assigned level. Assume that a call is made in the 1st level, and that the first idle finder is that assigned to the 7th level. Level marking relay LM<1> grounds wire 13 and the 1st terminal of the set NP2 in the finder CF7. Relays B, A pull up, but the holding circuit for relays B, C is not completed, and relay B falls back due to its short-circuiting by relay A. The vertical magnet VM now interacts with relay C until the 10th level is reached, when a looking circuit is closed over relays C (both windings), G (winding 2), B (winding 2), and wiper V1. Relay B does not operate, but relay G energizes and operates the release magnet ZM to restore the wipers to normal. Relays C, G fall back. and the vertical magnet VM raises the wipers to the 1st level, when the circuit for relay B (winding 2) in series with relay C (winding 1) over wiper V2 is completed, and the rotary magnet RM operates as described in the last paragraph in search of the calling line. Relay G is not how short-circuited over wiper VI, and energizes in series with relay C (winding 2), so that when release takes place, the release magnet ZM operates to restore the wipers to normal. Relay F energizes again, and the vertical magnet VM interacts with relay C to raise the wipers to the assigned level of the finder, when relay C holds over wiper V1, and relays F, C fall back in succession. If the finder is required to search over the 10th level, relay G is short-circuited over wiper V2 when this level is reached, and release does not occur. If the subscriber hangs up during vertical stepping, relay A releases and the finder stops opposite the level it has then reached. Call-finder assigned to the 10th level. Relay G is short-circuited over the 10th terminal of the set NP1 whenever relay F is energized. This produces the difference that when the finder is released after use on any other level, the rotary release magnet RZM operates. Relay F remains held, and the vertical magnet VM then operates to raise the wipers to the 10th level in the manner already described. In a modification of the call-finder circuits, relay B has only one winding corresponding to winding 2, and relay A is normally connected tc wire 13 to act as the starting relay.